STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
Cash flows from operating activities:
Net loss	$ (28,349)	$ (143,219)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	167	155
Stock-based compensation	4,082	4,075
Preferred stock issued in exchange a license agreement		119,045
Change in fair value of derivative liabilities	1,494
Issuance of common stock in a license agreement		87
(Increase) decrease in:
Receivables	(23)	431
Prepaid expenses and other current assets	(4,083)	(6,332)
Other noncurrent assets		1
Increase (decrease) in:
Accounts payable	(75)	23
Accrued expenses	246	(1,513)
Deferred revenue	(3,194)	(3,666)
Deferred rent	(65)	(239)
Net cash used in operating activities	(29,800)	(31,152)
Cash flows from investing activities:
Purchases of property and equipment	(385)	(257)
Net cash used in investing activities	(385)	(257)
Cash flows from financing activities:
Proceeds from exercise of stock options	98	551
Repurchase of restricted common stock	(1,042)	(853)
Repurchase of common stock		(2)
Proceeds from issuance of common stock, net of commissions and expenses of $2.7 million	47,270
Net cash provided by financing activities	46,326	(304)
Net decrease in cash and cash equivalents	16,141	(31,713)
Cash and cash equivalents, beginning of period	81,053	140,717
Cash and cash equivalents, end of period	97,194	109,004
Supplementary disclosure of cash flow information:
Cash paid for interest	0	0
Cash paid for income taxes	0	0
Series 1 Preferred Stock
Supplementary disclosure of noncash investing and financing activities:
Issuance of stock		$ 119,045
Payment of dividends in preferred stock	$ 9,036